Effects Of SLM And Annealing Process On Microstructure And Macroscopic Properties Of CoCrFeNiTi_0.6 High-entropy Alloy

With the rapid development of human society,human requirements for the properties and preparation process of alloy materials continue to increase.As a multi-component alloy material different from traditional alloys,high-entropy alloys generally have great hardness,excellent corrosion resistance and good thermal stability due to their unique structural characteristics.3D printing is an emerging process preparation method in recent years,which has great design freedom and ultra-high melting cooling rate,and can prepare high-density and high-strength alloys with grain refinement.Therefore,the majority of researchers focus on the research of using advanced 3D printing technology to prepare high-entropy alloys with excellent performance.However,so far,due to the complex working mechanism of 3D printing technology,the types of high-entropy alloys prepared are far smaller than the total number of high-entropy alloys that have been developed,and many studies mainly focus on several high-entropy alloy systems such as Co Cr Fe Ni and Co Cr Fe Ni Mn.Ti is the metal with the highest specific strength,and the addition of Ti elements is beneficial to the improvement of alloy hardness and strength.However,up to now,there has been no report of 3D printing technology to prepare CoCrFeNiTi high-entropy alloys.Based on the above analysis and the previous experimental experience,this paper prepared CoCrFeNiTi_0.6high-entropy alloy by 3D printing selective laser melting（SLM）process in terms of scanning speed,laser power and annealing temperature,and observed and analyzed its microstructure and macroscopic properties.The effects of scanning speed,laser power and annealing temperature on the microstructure and properties of CoCrFeNiTi_0.6high-entropy alloy were studied.The experimental results show that the OM images of CoCrFeNiTi_0.6high-entropy alloy under different parameters clearly display the scanning trajectory of the laser beam,and there are cracks,pores and other defects on the surface of the sample.The CoCrFeNiTi_0.6high-entropy alloy specimens prepared with different scanning speed and laser power were simple FCC face-centered cubic structures,and with the increase of scanning speed,the crystallinity of CoCrFeNiTi_0.6high-entropy alloy decreased,and the grains were refined.With the increase of laser power,the crystal plane spacing of CoCrFeNiTi_0.6high-entropy alloy increased,resulting in coarsening of the tissue.CoCrFeNiTi_0.6high-entropy alloy was still FCC single-phase structure after annealing at 450°C,but after annealing at 650°C and850°C,a large number of phases,R phases and Laves phases were generated.The CoCrFeNiTi_0.6high-entropy alloy specimen with low scanning speed and low laser power had a microstructure of submicron columnar crystal and equiaxed crystal.When either parameter of scanning speed and laser power increased,it led to a decrease in the columnar crystal ratio of the alloy sample and an increase in the equiaxed crystal ratio.And with the increase of annealing temperature,the structure of columnar crystal and equiaxed crystal changed,and new phases were generated.The elements of the high-entropy alloy under each laser scanning parameter were evenly distributed,and no element diffusion and aggregation occured.When any variable among the scanning speed,laser power and annealing temperature increased,the Vickers hardness and relative density of CoCrFeNiTi_0.6high-entropy alloy decreased,and the friction coefficient and wear rate increased.The details are as follows:with the increase of scanning speed,the Vickers hardness of the sample gradually decreased from 614.82HV to 547.82HV,the relative density gradually decreased from 96.98%to 95.65%,the average friction coefficient after stabilization gradually increased from 0.75 to 0.80,and the wear rate gradually increased from1.4835×10^-14m³/（N·m）to 1.7548×10^-14m³/（N·m）.With the increase of laser power,the Vickers hardness of the sample gradually decreased from 619.42HV to 446.46HV,the relative density decreased from 96.28%to 94.25%,the average friction coefficient after stabilization gradually increased from 0.78 to 0.84,and the wear rate gradually increased from 1.6188×10^-14m³/（N·m）to 2.2290×10^-14m³/（N·m）.With the increase of annealing temperature,the Vickers hardness of the sample decreased from 541.07HV to 345.78HV,the relative density decreased from 96.02%to 95.77%,and the wear rate gradually increased from 1.7480×10^-14m³/（N·m）to2.5039×10^-14m³/（N·m）.